1. Field of the Invention
The present invention relates in general to an electronic shopping system by which an order of products to be purchased by a user and the processing of clearing up a sum of products purchased by the user using a credit card can be safely carried out on a communication network, and more particularly to an electronic shopping method and an electronic shopping system by which an order of products to be purchased by a user and the processing of clearing up a sum of products purchased by the user using a credit card can be safely carried out using a cipher communication method.
2. Description of the Related Art
Until the present time, a large number of cipher communication methods have been proposed. These cipher communication methods are roughly classified into a method in which a key is held in common by utilizing a public key concept and a method in which the public key concept is not employed. For example, as for the method of employing the public key concept, there is well known a key distribution method based on a RSA cipher disclosed in an article of "A Method of Obtaining Digital Signatures and Public Key Cryptosystems" by R. L. Rivest, A. Shamir and L. Adleman, Communication of the ACM, Vol. 21, No. 2, pp.120 to 126, 1978, or public key distribution method disclosed in an article of "New Directions in Cryptology" by W. Diffice and M. Hellman, IEEE Transaction of the Information Theory, Vol. IT-22, No. 6, pp.644 to 654, 1976.
On the other hand, as for a method of not employing the public key concept, as disclosed in "ISO/IEC DIS 11770-2", pp. 1-23 there is well known a method including the following steps.
For example, it is assumed that three entities A, B and C are present on a communication network, and the entities A and C hold a key K(A, C) in common, and the entities B and C hold a key K(B, C)in common. In this connection, the entity C is assumed to be sufficiently reliable.
Step 1: Firstly, the entity A selects a key K at random, and then calculates a cipher text C(P) which has been obtained by enciphering a document P to be notified using the key K, i.e., C(P)=E(K: P). Now, E(K: P) shows the result of enciphering the document P using. the key K. In addition, the entity A calculates a cipher text C(K) which has been obtained by enciphering the key K using the key K(A, C), i.e., C(K)=E(K(A, C): K). Both C(P) and C(K) thus obtained are transmitted to the entity B through a communication network.
Step 2: The entity B transmits C(K) which has been supplied thereto through the communication network to the entity C.
Step 3: The entity C deciphers the key K using the key K(A, C) on the basis of K=D(K(A, C): C(P)). Now, D(K: P) shows the result of deciphering the document P using the key K. Next, the entity C calculates a cipher text C'(K) which has been obtained by enciphering the deciphered key using the key K(B, C), i.e., C'(K)=E(K(B, C): K), and then transmits the resultant C'(K) to the entity B.
Step 4: The entity B deciphers the key K from C'(K) using the key K(B, C) on the basis of K=D(K(B, C): C'(K)), and then deciphers the document P using the key K on the basis of P=D(K: C(K)).
In such a way, the entity B can obtain the contents of the document P.
A large number of cipher communication methods as described above have been proposed. If employing any one of those methods, an electronic shopping system can be designed which is such that by utilizing the communication network, a user purchases desired products from a retail store, and requests a credit card company of its payment. For example, in the above-mentioned method of not employing the public key, the user, the retail store, the credit card company, and the document may be made correspond to the entities A, B, C and a written order of the products to be purchased by the user, respectively.
According to a sort of electronic shopping system, in general, the user can order safely surely the desired products and also request the credit card company of its payment.
In the above-mentioned electronic shopping system, however, for example, there is a possibility that the following problem arises. That is, there is a possibility that since the credit card company can not authenticate the legality of the user, the retail store produces the false written order to send it to the credit card company.
In addition, there may be a case where the user does not desire that the contents of the products purchased by himself/herself become known to the credit card company. However, in the above-mentioned electronic shopping system, it is impossible that out of the contents of the document P corresponding to the written order, for example, only the information relating to the purchased products is not made become known to the credit card company.